For example, a panel for an automobile has a complicated shape, so that a mold process is divided into several steps, and the panel is molded by linearly arranged molds. In a transfer press or tandem press using such a plurality of presses, a panel transportation device is provided to sequentially transport members (panels) molded in a certain press to a subsequent press.
A crossbar type transportation device in Patent document 1 below has heretofore been widely used as the panel transportation device for the transfer press. In this device, a lift beam extending throughout press stations is provided so as to be able to ascend and descend in a line direction; a carrier is further suspended from the lift beam so as to be able to reciprocate among the respective stations in the line direction; a crossbar is set to the carrier; and a work grasp portion is attached to the crossbar, whereby work materials of the respective stations are simultaneously and intermittently transported.
Such a crossbar type transportation device has the following characteristics.
(1) Feed motion of a molded panel among mold stations is generated under motion control by cam driving or by an AC servo motor.
(2) The panel is transported by composite motion in a feed direction (horizontal direction) and a lift direction (vertical direction), and a vacuum cup attached to a transportation tool called the crossbar sucks and transports the panel.
(3) The crossbars among the mold stations are coupled both in the feed direction and the lift direction, and the respective crossbars are interlocked with each other and make totally the same motion.
(4) A feed arm which generates the feed motion among the stations is generally located on a front or rear side of a series of feed devices generally constituted of a carriage connecting the crossbars and of a link mechanism thereof, and the feed motion is generated by swinging the arm.
Furthermore, in addition to the crossbar type transportation device described above, there have been proposed panel transportation devices described in Patent documents 2 to 3 and the like below.
In a “transfer feeder” described in Patent document 2, a pair of lift beams moved up and down by a lifter is provided with a plurality of carriers which are independently self-propelled by a linear motor, and the linear motor is used as a drive source to enable high-speed transportation of a work (panel).
In a “transfer press transportation device” as is described in Patent document 1, a plurality of carriers is provided in a lift beam, and a servo motor is used as a drive source for the carriers to enable high-speed transportation of a work (panel).
A transport and positioning system described in Patent document 3 comprises a driver 40 having a lever mechanism 33 with an output portion 35 which drives and positions a crossbar 32, as shown in FIG. 1. This lever mechanism 33 has a swing arm 34 forming the output portion 35 at one end, and the output portion 35 is coupled to the crossbar 32. Further, the swing arm 34 is coupled at two points: a support point 38 and a drive point 43 distanced from each other. The distance between the support point 38 and the drive point 43 is shorter than a distance between the output portion and the support point. It is to be noted that in FIG. 1, 31 denotes a work grasp portion attached to the crossbar 32; 42 denotes a guide rod coupling a slide block 47 with the drive point 43; 51 denotes a swing motor which swings the guide rod 42; and 55 denotes a direct acting device which moves the slide block 47 up and down.
In this configuration, the slide block 47 is moved up and down by the direct acting device 55, and the swing motor 51 swings the guide rod 42 to drive/position a tip (the drive point 43) of the guide rod 42, and then this motion is enlarged by a leverage ratio to drive/position the crossbar 32 to which the work grasp portion 31 is attached.
Patent document 1: Japanese Patent Publication Laid-open No. 10-328766
Patent document 2: Japanese Examined patent publication No. 7-73756
Patent document 3: U.S. Pat. No. 6,382,400
However, the panel transportation devices described in Patent document 1 described above have the following problems: (1) the respective crossbars cannot have motions different from each other; (2) the servo motor and a feed driver are increased in size since the crossbars for all the stations are simultaneously moved; and (3) since motion curves for the respective press stations are the same, a mold shape needs to be specially designed to avoid interference, which causes difficulty in accommodating diversification of plate molding. Further, in a linear motor method of Patent document 2, high-speed feeding can be achieved by the linear motor, but a lift mechanism is additionally needed, and this method therefore has a problem that an entire structure is complicated and large. An AC serve method of Patent document 1 has a problem that high rigidity cannot be obtained due to a serial link.
Furthermore, in a swing arm method of Patent document 3, since the panel is transported by the swing arm, a longer transportation distance requires more length of the arm, and, for example, deflection of the arm causes vibration. Moreover, because the panel transportation device in Patent document 3 comprises a slide mechanism vertically driven among the press stations, this device cannot be applied to the multislide type transfer press without an upright for installation of the slide mechanism. Further, in order to correspond to complicated press molding, a tilting device needs to be separately provided in the crossbar to tilt the work grasp portion, and there is thus a problem that the structure is complicated and weight of movable portions is increased to make it more difficult to achieve a high speed.